1. Field of the Invention
The present invention generally relates to an antenna system, and more particularly to an antenna system with a matching conductive stub connected to a ground point.
2. Description of Related Art
Wireless sensor network is composed of sensor devices (e.g., Z-wave devices). The Wireless sensor network is commonly used to carry out home automation due to its simple structure, low power consumption and low cost.
A monopole antenna is ordinarily used in the sensor device to receive or transmit signals. Usually design of the monopole antenna requires large ground plane to achieve high antenna efficiency. However, there is a growing trend of the sensor devices towards miniaturization, resulting in small ground plane with low (e.g., less than 20%) antenna efficiency.
FIG. 1A shows a schematic diagram of a conventional monopole antenna. A shorted stub 13 is used to enhance antenna efficiency. FIG. 1B shows an equivalent circuit of the shorted stub 13 of FIG. 1A. The shorted stub 13 is conventionally used to match impedance in order to improve on antenna efficiency. However, the shorted stub 13 cannot improve the situation for compact sensor devices. Moreover, it increases area of a printed circuit board (PCB) for the worse.
A need has thus arisen to propose a novel scheme to overcome drawbacks of the conventional antenna system.